A coil assembly of an electrical inductive apparatus such as a transformer or an inductor is commonly constructed by winding an insulated conductor around a mandrill or cruciform a predetermined number of turns. The mandrill provides an opening in which a core material is eventually disposed and encircled by the coil assembly. In the case of a simple coil assembly without any taps for external connections, it is a fairly simple process to provide means for terminating and connecting the extreme ends of the insulated conductors to the outside environment. Many applications, however, require access to various portions of the coil assemblies. This would be the case, for instance, if a transformer or inductor has multiple taps for changing the turns ratio between the primary and secondary windings. In the past, this was accomplished by several different methods. When winding the coil and reaching a point that must be accessible, a terminal could actually be welded to the conductor itself. Conductors could then be attached and be coupled to a tap changer for ease in changing tap settings.
This method is appropriate for large, high power devices, those above 150 KVA, where the transformer may be immersed in oil and not readily accessible. However, if the transformer is open and inside an enclosure, as would be the case with a dry-type transformer, it would be more cost effective to have direct, manual interconnections of the conductors, right at the transformer coil itself. A simpler method would be to form a terminal in the shape of a loop from the conductor itself during the winding process. This would then allow for a nut and bolt connection through a ring lug or similar arrangement attached to a conductor to secure the conductor to the formed terminal. This method requires that the formed terminals have sufficient surface areas that have been carefully formed and modified to remove any insulation at the point of contact. Hot spots could occur if this is not done properly since the connection is a current carrying point. Care must also be taken when attaching the conductor to the tap to prevent external damage to the coil itself.
It would therefore be desirable to provide a new and improved terminal structure for an electrical inductive apparatus, such as a power transformer or inductor. The terminal structure would enable simple tap changes to be made on the face of the coil, in the field where the apparatus is installed. Connections to the terminal would require a minimum amount of hardware to secure the conductor to the terminal or tap.